The originally confidential report was publicized hours after US President Barack Obama expressed skepticism on sending more troops to Afghanistan in a tour of the TV talk shows Sunday.

It was sent to the White House in late August and is currently under review. It comes as President Obama faces difficult choices on how to best prosecute a war that has become increasingly unpopular amid a rising body count and a pack of other domestic priorities.

Obama came into office pledging to refocus American military might on Afghanistan, which harbored and trained the terrorists that carried out the 9/11 attacks.

But a growing chorus of critics now says the US risks becoming bogged down in a grinding war of attrition with the Taliban, as it tries to train and prop up Afghan security forces whose capabilities lag far behind even Iraq's.

In one section of the report, McChrystal warns: "The campaign in Afghanistan has historically been under-resourced and remains so today -- ISAF [the International Security Assistance Force in Afghanistan] is operating in a culture of poverty ... Consequently, ISAF requires more forces."

Failure to boost troop numbers and turn around the situation in the next year "risks an outcome where defeating the insurgency is no longer possible," the Post cited McChrystal as saying, citing his unclassified assessment.

McChrystal concludes the document's five-page Commander's Summary on a note of muted optimism: "While the situation is serious, success is still achievable."

But he repeatedly warns that without more forces and the rapid implementation of a genuine counterinsurgency strategy, defeat is likely. McChrystal describes an Afghan government riddled with corruption and an international force undermined by tactics that alienate civilians.

He provides extensive new details about the Taliban insurgency, which he calls a muscular and sophisticated enemy that uses modern propaganda and systematically reaches into Afghanistan's prisons to recruit members and even plan operations.

Meanwhile, Obama on Sunday expressed doubts on giving McChrystal more troops, saying the US' overall strategy in Afghanistan was still under review, according to a Reuters roundup on those appearances.

"I just want to make sure that everybody understands that you don't make decisions about resources before you have the strategy ready," he told ABC.

He told NBC's "Meet the Press" that it was important for him to exercise skepticism when sending an American in uniform into harm's way.

"Because I'm the one who's answerable to their parents if they don't come home. So I have to ask some very hard questions any time I send our troops in," he said.

He said that while he did not have a deadline for withdrawing U.S. forces from Afghanistan, "I'm certainly not somebody who believes in indefinite occupations of other countries."

The US is already in the midst of a massive troop buildup in Afghanistan, with Obama having approved a deployment of an additional 21,000 troops this year. (See here for a map from February showing locations of planned troop buildups).